Modular coil assembly

ABSTRACT

In various specific embodiments, a localizer can include a plurality of coil groups, where each coil group includes three coils that are formed around a single center. Each of the three coils can be formed around separate jigs and the jigs can be interconnected to form the coil group. The jigs need not be annular, but may be formed in any appropriate configuration of shape or geometry for forming the final coil group.

FIELD

The subject disclosure relates to a system for forming a structure, andparticularly to a structure for forming a coil.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

A system for determining a location of a tracking device can include alocalizer that is configured to emit or generate an electromagneticfield. The electromagnetic field may be sensed by the tracking deviceand a location of the tracking device may be determined based upon thesensed electromagnetic field. The electromagnetic field may vary over avolume and this variance can be used to determine the location of thetracking device. The localizer device may be formed to include a coil ofwire to generate the electromagnetic field once a current is driventhrough the coil of wire. Forming the localizer array, however, mayrequire several forming and processing steps.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

A localizer can be formed to generate an electromagnetic field for usein a tracking system that may track a device for a navigation system.That navigation system may include a surgical navigation system to beused with computer-aided surgery. The navigation system may be used tonavigate an instrument during a procedure. The localizer can be formedas a transmitter array to include one or a plurality of coils in aspecified design.

The coils can be formed to have a common center, but each coil beingformed to emit a field having a selected shape and/or intensity.Including a plurality of coils can increase the diversity of the fieldfor increasing possible sensitivity for determining the location of atracking device. It is understood, however, that a plurality of coilsmay be placed in a coil array where none or less than all share acenter. For example, a coil may be formed on a jig and laid flat withother coils placed adjacent to it, but not including a common center.

In various specific embodiments, a coil array can include a plurality ofcoil groups, where each coil group includes three coils that are formedaround a single center. Each of the three coils can be substantiallyorthogonal to one another in a final assembly. Each of the three coilscan be formed around separate jigs and the jigs can be interconnected toform the coil group. It is understood, however, that the coil group neednot share a center and the coil group need not be orthogonal to oneanother. The jigs need not be annular, but may be formed in anyappropriate configuration of shape or geometry for forming the finalcoil group. Generally, each of the coils of wire can be formed in a jigthat is formed with a selected shape.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a view of a navigation and imaging system;

FIG. 2 is a detail transparent view of a transmitter coil array,according to various embodiments;

FIG. 3A is an exploded view of a coil group, according to variousembodiments;

FIG. 3B is an exploded view of a coil group, according to variousembodiments;

FIG. 4 is an assembled view of a coil group, according to variousembodiments;

FIG. 5A is a process view of assembling two coil jigs, according tovarious embodiments;

FIG. 5B is a process view of assembling two coil jigs with a third coiljig, according to various embodiments;

FIG. 6 is a perspective view of a single coil jig, according to variousembodiments;

FIG. 7A is a side plan view of a single coil jig, according to variousembodiments;

FIG. 7B is a detail cross-sectional view of a wrapped jig of FIG. 7A;and

FIG. 8 is a side plan view of a single coil jig, according to variousembodiments.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

A localizer of an electromagnetic (EM) navigation system may include atransmit coil array (TCA). Although the localizers referred to and/ordisclosed herein are primarily described as including TCAs (or coilarrays) for transmitting signals (such as emitting or generating anelectromagnetic field), the TCAs may be used for receiving signals. TheTCA can include multiple sets or groups of coils of conductive material(e.g. wire) for generating the electromagnetic field and may begenerally referred to as electromagnetic (EM) coils. Each set of the EMcoils may include three orthogonally positioned coils that are used togenerate EM fields. Other arrangements are envisioned within the scopeof the subject disclosure. Orthogonally positioned coils have respectivecenter axes that are at right angles relative to each other. Also, theaxis of all of the coils may intersect at only one point. EM navigationmay be enhanced and or performed after a precise and lengthy calibrationprocess for calibrating the TCA. The calibration process can also causea “bottleneck” in a manufacturing process of a navigation system.

The calibration process is primarily performed due to inconsistencies,irregularities, and variances between different TCAs. This includesdifferences in coil placements, number of windings of each coil, lengthsof coil wires, sizes of coils, spacing between coils, etc. Thedifferences between coils in the TCA's generally leads to the fieldsproduced by different TCAs to be different. Generally, calibration,therefore, may include factory or prior to use calibration. Thecalibration may include determining the field or mapping the fieldproduced by each produced TCA, due to manufacturing variances of thecoils, to determine the field strengths at different locations relativeto the TCA. Accordingly, coil groups, formed as discussed below, mayinclude a variance in field produced from one coil to another that issmall or within an error of a navigation system so as to beimperceptible difference (as measured during a calibration process)relative another coil portion or group produced in the same manner.Thus, calibration may be reduced or eliminated. The following disclosedimplementations provide TCAs that can lessen calibration processes ofTCAs and/or eliminate the need for calibrating TCAs. An example EMnavigation system 202 is shown in FIG. 1. The EM navigation system 202may include any of the TCAs, including the coils discussed therewith,shown and/or described herein. It is understood that the formation ofvarious components, including jigs or windings, as discussed herein mayinclude those disclosed in U.S. Pat. App. Pub. No. 2014/0323852,incorporated herein by reference. For example, additive manufacturing or“3D” printing may be used to form jigs for TCAs, as discussed herein.

Although the EM navigation system 202 is primarily described withrespect to performing a procedure on a human patient, the EM navigationsystem 202 may be used to perform a procedure on other animate and/orinanimate subjects. Also, the implementations disclosed herein may beapplied to other EM systems and for purposes other than for positiontracking of devices. For example, the implementations may be used togenerate EM fields in a transcranial magnetic stimulation system. Also,procedures disclosed herein can be performed relative to a volume, amechanical device, and/or an enclosed structure. The volume may be of ananimate or inanimate object. The subject can be an object that includesan enclosed mechanical device.

With reference to FIG. 1, an instrument assembly may include anappropriate tool or instrument, such as one including a handle or motorand a toolbit. The instrument 20 may include a portion that ispositioned relative to, such as within, a skull 150 of a subject 152.The tool assembly 20 may include a tracking device 30 and may be anavigated instrument. As discussed above, the instrument 20 is merelyexemplary, and other navigated instruments may include catheters, leads,stimulators, etc. Also, the tracking device 30 may be incorporated intoa separate element, such as a removable stylet. The stylet may be placedwithin a lumen of a catheter.

The tracking device 30 may be interconnected with the navigation system202. The navigation system 202, as discussed further herein, may includea tracking system 204 that can track the tracking device 30 in sixdegrees of freedom, including three-dimensional space including a X, Y,Z location and various orientations to determine a position of thetracking device 30 in space. As illustrated above, the instrument 20 mayinclude the tracking device 30 that allows for directly tracking thetool 20 during an implantation and positioning of tool 20. Appropriatetracking devices can include tracking devices as disclosed in U.S. Pat.No. 8,644,907, incorporated herein by reference. Additionally, thenavigation system can include the navigation system disclosed in U.S.Patent Application Publication 2014/0323852, incorporated herein byreference.

With continuing reference to FIG. 1, the tool 20 may be used to form anopening or bore 210 in the skull 150 of the subject 152. The bore 210may be a burr hole formed through the skull 150 as generally understoodin the art. The tool 20 may be tracked either directly via the trackingdevice 30 or via the tracking device on a stylet or other portionassociated with the tool 20. Further, as noted above, the trackingdevice 30 may be associated directly with the tool tip or with anotherportion of the tool assembly 20. Thus, any one or more of these may beused to track the selected portion of the tool assembly 20.

The navigation of the tool assembly 20 relative to the subject 152 mayproceed according to various navigation procedures and techniques, suchas those generally known in the art and discussed below, to ensure orassist in positioning the catheter 10 in a selected, including apredetermined or preselected location, within the subject 152. Further,although the following description is related generally to positioningthe tool assembly 20 relative to the skull 150 of the subject 152, othernavigated procedures may be performed.

The navigation system 202, which may include an electromagneticnavigation system, is primarily described with respect to performing aprocedure on a human patient, the navigation system 202 may be used toperform a procedure on other animate and/or inanimate subjects,including those navigation systems as disclosed in U.S. Pat. App. Pub.No. 2014/0323852, incorporated herein by reference. Also, proceduresdisclosed herein can be performed relative to a volume, a mechanicaldevice, and/or an enclosed structure. The volume may be of an animate orinanimate object. The subject can be an object that includes an enclosedmechanical device.

The navigation system 202 assists in performing a navigated or guidedprocedure. The guided procedure can be, for example, a surgicalprocedure, a neural procedure, a spinal procedure, and an orthopedicprocedure. The navigation system 202 allows a user, such as a surgeon220, to view on a display 256 a position of the tool assembly 20 in acoordinate system. The coordinate system can be related to an image,such as in an image guided procedure, or can be related to an imagelessprocedure.

The navigation system 202 can operate as an image-based system or as animageless system. While operating as an imageless system, the navigationsystem 202 can register a subject space (generally defined within andnear the subject 152) to a graphical display representing an area of thesubject 152, rather than to both the subject space and an image space.Image data of the subject 152 need not be acquired at any time, althoughimage data can be acquired to confirm various locations of instrumentsor anatomical portions of the subject 152. Positions of the subject 152can be tracked and positions of the tool assembly 20 relative to thesubject 152 can be tracked.

While operating as an imageless system, a position of an anatomicalstructure can be determined relative to the instrument and the positionsof the anatomical structure and the instrument can be tracked. Forexample, a plane of an acetabulum can be determined by touching severalpoints with the tool assembly 20, or selected tracked tool with at leastone of the tracking devices 30. As another example, a position of afemur can be determined in a similar manner. The position of the toolassembly 20 and the anatomical structure can be shown on a display withicons or graphics. The display, however, may not show actual image datacaptured of the subject 152. Other data can be provided, such as atlasdata or morphed atlas data. The atlas data can be image data that isgenerated or generalized from the subject 152. For example, a brainatlas can be generated based on detail analysis of image data of a brainof a patient. Operation of the navigation system 202 as an image basedsystem is further described below.

Although the navigation system 202 is described as acquiring image datausing an imaging device 230, other data may be acquired and/or used,such as patient and non-patient specific data. The imaging device 230acquires pre-, intra-, or post-operative image data and/or real-timeimage data of a subject 152. The imaging device 230 can be, for example,a fluoroscopic x-ray imaging device that may be configured as a C-armhaving an x-ray source 232 and an x-ray receiving device 234. Otherimaging devices may be included and mounted on the imaging device 230.Calibration and tracking targets and radiation sensors may be includedwith the imaging system 230.

The navigation system 202 may further include an imaging devicecontroller 236. The imaging device controller 236 controls the imagingdevice 230 to (i) capture x-ray images received at the x-ray receivingsection 234, and (ii) store the x-ray images. The imaging devicecontroller 236 may be separate from the imaging device 230 and/orcontrol the rotation of the imaging device 230. For example, the imagingdevice 28 can move in selected directions around the patient 152. Also,the imaging device may include an O-arm® imaging device as sold byMedtronic, Inc., having a place of business in Minnesota.

Further, an imager tracking device 240 may be included to track aposition of selected portions of the imaging device 230 to identify theposition of the imaging device 230 relative to the subject 152 whileacquiring the image data to assist in registration. The image data canthen be forwarded from the imaging device controller 236 to a processingmodule of a navigation computer 250 wirelessly or via a link 252. Thenavigation computer 250 can include a processing module that isconfigured to execute instructions to perform a procedure.

A work station 254 can include the navigation computer 250, a navigationdisplay 256, a user interface 258, and an accessible memory system 260.The image data may be transmitted from the controller 236 to the workstation 254 or to a tracking system 204. The workstation 254 may be aportable computer, such as a laptop computer or a tablet computer. Thenavigation computer 250 including the computer module may include ageneral purpose processor that executes instructions for navigating thetool assembly 20 and/or may include an application specific circuit. Thetracking system 204, as discussed further herein, may include a coilarray controller (CAC) 260 having a navigation device interface (NDI)262.

While the imaging device 230 is shown in FIG. 1, any other alternative2D, 3D or 3D imaging acquired over time to include four dimensions,imaging modality may also be used. Examples include those discussedabove, and further any imaging device, such as isocentric fluoroscopy,bi-plane fluoroscopy, ultrasound, computed tomography (CT), multi-slicecomputed tomography (MSCT), T1 weighted magnetic resonance imaging(MRI), T2 weighted MRI, high frequency ultrasound (HIFU), positronemission tomography (PET), optical coherence tomography (OCT),intra-vascular ultrasound (IVUS), ultrasound, intra-operative, computedtomography (CT), single photo emission computed tomography (SPECT),and/or planar gamma scintigraphy (PGS) imaging devices may be used. Anyof these imaging devices may be used to acquire pre- or post-operativeand/or real-time images or image data of the subject 152. The images mayalso be obtained and displayed, generally, in two or three dimensions.In more advanced forms, 3D surface rendering regions are achieved of thesubject, which may be rendered or changed in time (fourth dimension).The 3D surface rendering regions may be achieved by incorporatingsubject data or other data from an atlas or anatomical model map or frompre-operative image data captured by MRI, CT, or echocardiographymodalities. Image data sets from hybrid modalities, such as positronemission tomography (PET) combined with CT, or single photon emissioncomputer tomography (SPECT) combined with CT, can also providefunctional image data superimposed onto anatomical data to be used toreach target sites within the subject 152.

The navigation system 202 further includes the tracking system 204. Thetracking system 204 includes a localizer 264, which may also be referredto as a transmit coil array (TCA), a tracking array, or a transmit coilassembly. The TCA 264 includes one or more coil groups or sets 266, asdiscussed further herein, that can transmit or receive a signal and/orgenerate a field. The tracking system 204 may include the CAC 260, thelocalizer 264, and the instrument tracking device 30 of the toolassembly 20. It is understood that the tracked portion may be generallyreferred to as an instrument and that the tracking device may begenerally referred to as an instrument tracking device. The trackingsystem may also track a dynamic reference frame (DRF) 270. All trackedportions are connected to the CAC 260 via the NDI 262. The CAC 260 andthe NDI 262 can be provided in a CAC/NDI container 272. The NDI 262 mayhave communication ports that communicate with the localizer 264, theinstrument tracking device 30 and/or the DRF 270 wirelessly or viawires.

The coil arrays localizer 264 can transmit signals that are received bythe DRF 270 and at least one tracking device 271 (e.g., the instrumenttracking device 30). The tracking device 30 can be associated with thetool assembly 20 at a location that is generally positioned within thesubject 152 during a procedure. The DRF 270 can then transmit and/orprovide signals, from the DRF tracking device 271, based upon thereceived/sensed signals of the generated fields from the localizer 264and/or other localizers. It is understood that the tracking system mayalso be operated in reverse, where the tracking devices 30, 271 transmita field that is sensed by the TCA 264.

The DRF 270 can be connected to the NDI 262 to forward the informationto the CAC 260 and/or the navigation computer 250. The DRF 270 may befixed to the subject 152 and adjacent to the region where navigation isoccurring such that any movement of the subject 152 is detected asrelative motion between the localizer 264 and the DRF 270. The DRF 270can be interconnected with the subject 152. Any relative motion isindicated to the CAC 260, which updates registration correlation andmaintains accurate navigation.

In operation, the navigation system 202 creates a map between points inimage data or an image space, such as one defined by an image 280 shownon the display 256, and corresponding points in a subject space (e.g.,points in an anatomy of a patient or in a patient space). After the mapis created, the image space and subject space are registered to eachother. This includes correlating position (location and orientations) inan image space with corresponding positions in a subject space (or realspace). Based on the registration, the navigation system 202 mayillustrate an icon 282 (which may include a three-dimensional renderingof the instrument, including the tool assembly 20) at a navigatedposition of the tool assembly 20 relative to an image of the subject 152in a super-imposed image. For example, the icon 282 can be illustratedrelative to a proposed trajectory and/or a determined anatomical target.The work station 254 alone and/or in combination with the CAC 260 and/orthe C-arm controller (or control module) 236 can identify thecorresponding point on the pre-acquired image or atlas model relative tothe tracked tool assembly 20; and display the position on display 256and relative to the image 280. This identification is known asnavigation or localization. The work station 254, the CAC 260, and theC-arm controller 236 and/or selected portions thereof can beincorporated into a single system or implemented as a single processoror control module.

To register the subject 152 to the image 280, the user 220 may use pointregistration by selecting and storing particular points from thepre-acquired images and then touching the corresponding points on thesubject 152 with a pointer probe or any appropriate tracked device. Thenavigation system 202 analyzes the relationship between the two sets ofpoints that are selected and computes a match, which allows for acorrelation of every point in the image data or image space with itscorresponding point on the subject 152 or the subject space.

The points that are selected to perform registration or form a map arethe fiducial markers, such as anatomical or artificial landmarks. Again,the fiducial markers are identifiable on the images and identifiable andaccessible on the subject 152. The fiducial markers can be artificiallandmarks that are positioned on the subject 152 or anatomical landmarksthat can be easily identified in the image data.

The navigation system 202 may also perform registration using anatomicsurface information or path information (referred to asauto-registration). The navigation system 202 may also perform 2D to 3Dregistration by utilizing the acquired 2D images to register 3D volumeimages by use of contour algorithms, point algorithms or densitycomparison algorithms.

In order to maintain registration accuracy, the navigation system 202tracks the position of the subject 152 during registration andnavigation with the DRF 270. This is because the subject 152, DRF 270,and localizer 264 may all move during the procedure. Alternatively thesubject 152 may be held immobile once the registration has occurred,such as with a head holder. Therefore, if the navigation system 202 doesnot track the position of the subject 152 or an area of an anatomy ofthe subject 152, any subject movement after registration would result ininaccurate navigation within the corresponding image. The DRF 270 allowsthe tracking system 204 to track the anatomy and can be used duringregistration. Because the DRF 270 is rigidly fixed to the subject 152,any movement of the anatomy or the localizer 264 is detected as therelative motion between the localizer 264 and the DRF 270. This relativemotion is communicated to the CAC 260 and/or the processor 250, via theNDI 262, which updates the registration correlation to thereby maintainaccurate navigation.

The tracking system 204 can position the localizer 264 adjacent to thepatient space to generate an EM field (referred to as a navigationfield). Because points in the navigation field or patient space isassociated with a unique field strength and direction, the trackingsystem 204 can determine the position (which can include location andorientation) of the tool assembly 20 by measuring the field strength anddirection or components of the EM field at the tracking device 30. TheDRF 270 is fixed to the subject 152 to identify the location of thesubject 152 in the navigation field. The tracking system 204continuously determines the relative position of the DRF 270 and thetool assembly 20 during localization and relates this spatialinformation to subject registration data. This enables image guidance ofthe tool assembly 20 within and/or relative to the subject 152.

To obtain a maximum accuracy it can be selected to fix the DRF 270 ineach of at least six degrees of freedom. Thus, the DRF 270 or anytracking device, such as the tracking device 30, can be fixed relativeto axial motion X, translational motion Y, rotational motion Z, yaw,pitch, and roll relative to a portion of the subject 152 to which theDRF 270 is attached. Any appropriate coordinate system can be used todescribe the various degrees of freedom. Fixing the DRF 270 relative tothe subject 152 in this manner can assist in maintaining maximumaccuracy of the navigation system 202.

The tool assembly 20 can include the stylet, drill, etc., as discussedabove. Thus, reference to the tool assembly 20 is not intended to limitthe instrument that may be tracked and navigated. With reference to anyappropriate navigated instrument, it may include the tracking device 30that may include the power source 66 and generator 70. The power supplymay be charged, as discussed above, and the tool may be tracked with thenavigation system as discussed above.

The navigation system 202, as discussed above, includes the TCA 264 thatmay have one or more coil sets or groups 266. With continuing referenceto FIG. 1, and additional reference to FIG. 2, the TCA 264 may includethe coil groups 266 formed of various coil elements or portions,including a first large coil portion 300, a second medium coil portion302, and a third small coil portion 304. Each of the coil portions300-304 may be manufactured separately and assembled together, and thesize designation or number designation is only for ease of the currentdiscussion, unless specifically noted otherwise. The coil portions300-304 may be positioned to generate a field of substantiallyorthogonal to one another, but around a common center 310. As disclosedabove, however, a common center is not required, even when theindividual coils are formed on jigs, as discussed herein. In otherwords, as illustrated in FIGS. 2 and 4, each of the coils has arespective axis 300 a-304 a around which the coil is wound. All of theseaxes intersect at only one point, which is the center 310. Further, thecoil groups 266 can include a first coil group 266A, a second coil group266B, and a third coil group 266C.

It is understood, however, that the TCA or localizer 264 can include anyappropriate number of the coil groups such as four of the coil groups266. Additional coil groups may be used for redundancy and accuracy oftracking. Further, it is understood that each of the coil groups neednot include the three coil elements 300-304, but may generally includethree to provide a selected degree of information, such as includingsix-degree of freedom information, relating to or for determining thelocation of the tracking device 30 associated with the instrument 20.Further, it is understood that the TCA 264 need not be provided as aseparate or movable portion or member, such as within a casing 312, butmight be formed as a portion of a patient support 314 or otherappropriate portion positioned relative to the subject 152.Nevertheless, for the following discussion, the TCA 264 is exemplarilyillustrated as a movable unit including three of the coil groups 266,where each of the coil groups includes three coil elements or portions300-304.

It is understood that each of the coil groups, 266A-266C can includethree individual coil elements for generating a field relative to thesubject 152 or any appropriate volume. As noted above, the field cangenerally define or form a navigation space that allows for the trackingdevice 30 to be tracked within the navigation volume of space. Thisvolume of space can include a subject space, such as a selected space ofthe subject 152 including within the skull 150 of the subject 152. Thesubject space can be generally positioned within the navigation space,and the navigation space can then be registered to the image space,again as noted above. This allows for registration of the navigationspace to the image space and allows for display of the icon orrepresentation of the instrument 282 relative to the image 280 of thesubject 152 on the display device 256.

The coil groups, such as the group 266A, can include the three coilelements 300, 302, and 304. Each of the coil elements can generallyinclude a jig or coil form, including a large coil form 320 for thelarge coil element 300. A medium coil jig or form 322 for the mediumcoil element 302, and a small coil form or jig 324 for the small coilportion 304. Each of the jigs 320-324 may be formed according to variousmanufacturing techniques, such as casting, additive manufacturing, rapidprototyping, 3-D printing, injection molding, machining, or the like. Asan example, the jigs may be formed using, for example,stereolithography. As another example, alumina ceramic may be printedusing a stereolithography process or a cast process to form one or moreof the jigs. The jigs may be formed of selected materials, including,nylon, polyvinylchloride, polycarbonate, polyester, polysulphone,polyphenylenesulphone, polyetheretherketone, polyphenylene, sulphide,polyetherimide, polyamide-imide, and/or polybenzimidazole. The materialsof the jigs may have coefficients of thermal expansion that are lessthan predetermined values. Various manufacturing techniques andmaterials can include that disclosed at U.S. Patent ApplicationPublication 2014/0323852, incorporated herein by reference.

The jigs 320-324 can be formed to include various geometries andconfigurations such as annular, circular, square, octagonal, hexagonal,or other appropriate configurations. According to various embodiments,the jigs 320-324 are generally inert and/or invisible to any EM fieldgenerated with a coil formed on the jigs 320-324. Further, asillustrated herein, each of the jigs may have an internal surface thatforms a hollow or void. Thus, each of the coil portions 300-304generally include an air core or equivalent thereto. In other words, thejig portion on which the coils are wound does not affect the fieldproduced by the coil, even if the coil remains on the jig during use.The coil generally includes a wire, as discussed herein, which is woundon the respective jig 320-324. A current driven through the wiregenerates the EM field. The wire is generally wound on an exteriorsurface of the respective jig 320-324.

Generally, as illustrated in FIG. 3, each of the coil jigs 320-324 canbe generally octagonal, including non-regular sides. The non-regularoctagons can include eight sides, where each of the sides includes adifferent length or, as illustrated in FIG. 3, each of the coil jigs320-324 can include four short generally equally length sides and fourother sides. In the various jigs, the four remaining sides of theoctagon may have two sides of the same length and two more of a samelength, but different than the other two. In other words, each of thejigs may be generally square with faceted or straight corners. Theoctagonal shape assists in forming the coil of wire around the jig, asdiscussed herein. Further, the octagonal shape assists in modeling thefield formed by the coil formed on the respective jig 320-324. Forexample, the faceted corners can allow the wire to wrap more evenly andprecisely, such as following the shape of the jig more closely. Complexshapes or shapes with sharp edges or corners may not allow the coil tobe wrapped as discretely and may affect the shape of the coil, thusmaking modeling of the field more difficult.

As an example, with reference to the jig 320, it may include fourgenerally equal length short sides 320 a, 320 b, 320 c and 320 d. Eachof the short sides 320 a-320 d may be generally the same length. Twomedium length sides 320E and 320F may extend between adjacent shortsides, such as short side 320 a and 320 d and 320 b and 320 c. A finaltwo long sides 320 g and 320 h may be longer than the two medium lengthsides 320 f and 320 e, but the two long sides 320 g and 320 h may alsobe at the same length. The jig 320 may further include an exteriorsurface 354 and an opposed exterior surface 355. Generally, as discussedherein, the coil is formed between the two exterior surfaces 354, 355.

It is understood, however, that the other jigs may be formed in asimilar configuration or a different configuration. For example, thesmall jig 324, may have four short sides of generally equal length orequal length, and four other sides that are longer than the short sides,but also of generally equal length. Nevertheless, each of the jigs320-324 may include a generally equivalent geometry as illustrated anddiscussed herein. Further, each of the jigs may include opposed exteriorsurfaces between which the coil is formed.

The octagonal configuration of the jigs 320-324 may allow for forming afield having a geometry and field strength of a selected shape andconfiguration. The jigs may be further formed, such as in depth of themain coil channel, diameter, etc. to create a field diversity to assistin identifying a location of the tracking device 30. The octagonalgeometry, however, may also allow for ease of repeatability betweendifferent production runs of the jigs and/or coil windings (as discussedfurther herein and above). The field strength can be determined over thenavigation volume, but include a field strength variability to allow forprecise and/or efficient calculation of the location of the trackingdevice 30. It is understood that other possible shapes for the jigs320-324 may form different field shapes and require and/or allow fordifferent field or tracking preciseness.

As illustrated in FIGS. 3A-3B, each of the jigs 320-324 may furtherinclude additional geometry besides an external perimeter geometry. Forexample, as illustrated in FIG. 2, the three coil portions 300-304 willbe assembled into a single assembly to form one of the coil groups 266.Therefore, each of the jigs may include portions that assist inassembling the three coil portions 300-304 into the single coil group266A that includes the common center 310.

The first or large jig 300 may include a first coil portion receivinggroove or depression 330 and a second coil receiving portion 332. Thegrooves 330, 332 can be recesses that are generally opposed to oneanother and formed in an inner surface 334 and extending towards anouter surface 336 of the jig portion 320. The recesses or grooves 330,332 can extend a dimension, such as a depth of the jig 320. As discussedfurther herein, this can allow the other jig members, such as the jig322 to slide into the respective recesses 330, 332 for assembly of thecoil group.

The medium sized jig member 322 may include grooves or recesses,including a first recess 340 and a second recess 342. The recesses canbe opposed to one another and formed as depressions in an inner wall orsurface 344, where the depression extends towards the outer wall orsurface 346. Further, the medium jig member 322 can include one or morestops, such as two stops 348 and 350. The stops 348, 350 can extend fromthe exterior wall surface 346. As discussed further herein, the stops348, 350 can engage a surface, such as an upper side surface 354 of thelarge jig member 320 to assure or assist in achieving a proper (i.e.predetermined and selected) position of the second jig member 322relative to the first jig member 320. It is understood that additionalstops or different formations of the stops 348, 350 can be provided toengage the jig member 320. Further, it is understood that stops 348, 350need not be required but may be included for assembly ease and/orconfirmation. Further, the stops 348, 350 may allow for achieving smallor tight tolerances in forming the coil groups.

The third jig member 324 may include stops 360 and 362 similar to thestops 348 and 350 of the second jig member 322. The stops 360, 362 onthe third jig member 324 can extend from an exterior surface 364 of thethird jig member 324 and could be sized and configured to have selectedsides be received within the depression 340 and 342 of the second jigmember 322. The stops 360 and 362 can stop or position the third jigmember 324 relative to the second jig member 322. Similarly, the stops348, 350 can stop movement of the second jig member 322 into the firstjig member 320, or sides of the second jig member 322 are sized andconfigured to be received in the depressions 330, 332.

With continuing reference to FIGS. 2, 3A, and 3B, and further referenceto FIG. 4, the coil group 266 a is illustrated in an assembledconfiguration, but not in the coil array 264. The coil group 266 aincludes the first jig or coil portion 300 having inserted it therein,the second coil portion 302, having inserted therein the third coilportion 304. As illustrated in FIGS. 5A-5B, the process of assemblingthe coil portions 300-304 can be sequential to achieve the configurationillustrated in FIG. 4. Nevertheless, as illustrated in FIG. 4, themedium jig 302 may receive the first small jig 304 in the respectivegrooves 340 and 342. The stops, including stop 360, may engage anexternal surface 370 of the second jig 322 to stop or position the thirdjig 304 relative to the second jig 302. Once assembled, the second jig322 can then be positioned within the respective grooves 330, 332 of thefirst jig 320. The stops 348, 350 can then engage the surface 354 of thefirst jig member 300 to position the second jig 322 relative to thefirst jig 320.

According to various embodiments, therefore, as illustrated in FIG. 5A,the coil group 266 can be assembled form the several coil portions300-304. The various depressions 330, 332, 340, 342 and stops 348 and360 can assist in assuring the selected or designed alignment. Forexample, as noted above the stops 348, 360 may assure the common center310 of the coil group 266. It is understood, however, as discussedabove, that other configurations may be selected and designed. Thus, thedepressions and stops may be provided to assure the selectedconfiguration.

In the assembly process, the first jig 324 as the first coil portion 304can be slid along exterior sidewall surfaces 324A and 324B into therespective grooves or depressions 340 and 342 of the second jig member322 generally in the direction of the arrow 374. The third jig member324 can be moved into the depressions 340, 342 until the stops 360 and362 engage the exterior side surface 370 of the second jig member 322.Once the stops 360 and 362 engage the surface 370, a user may know thatthe third jig member 324 is properly seated or selectively (e.g.predetermined) positioned relative to the second jig member 322. Thesecond jig 322 and the third jig 324 can be coupled in any appropriatemanner such as with an adhesive, a snap fit, or fastener to connect twoor more of the jigs 320-324

In various embodiments, it is understood, however, that a controlledmechanism, such as a robotically controlled mechanism, can preciselyposition the third jig member 324 relative to the second jig member 322by knowing the three-dimensional location of both of the third jigmember 324 and the second jig member 322. Therefore, the physical stops360 and 362 may not be required, but are illustrated for the currentdiscussion. The assembly may also occur during production and formationof the coil portions 302 and 304 with a machine controlled assemblyline.

A coil group sub-assembly is formed, which may include the third jigmember 324 being is inserted and assembled into the second jig member322 to a selected position, such as when the stops 360 and 362 engagethe surface 370. The coil group sub-assembly (including the assembledsecond jig member 322 and third jig member 324) can be inserted into thefirst jig member 320, as illustrated in FIG. 5B. The assembly of thesecond jig member 322 and the third jig member 320 can include generallymoving the second jig member 322 in the direction of arrow 376. Thesecond jig member 322 is positioned or slides the exterior wall surface380 and 302 into the respective grooves 330 and 332 of the first jigmember 300. The second jig member 302 can be positioned or moved in thedirection of arrow 376 until the stop members 348 and 350 engage thesurface 354 of the first jig member 320. Again, the stops 348 and 350can allow for the user or the individual assembling the coil group 266to determine that the proper position and configuration of the coilmembers 300-304, including the jigs 320-324, has been achieved.

The stops, including the stops 348, 350, 360, 362 assist in ensuring aproper assembly of the coil group 266. The stops may only allow anassembly in one direction of the coil portion. This can ensure that thefield is generated according to generally known or predeterminedparameters. Further, as illustrated in the FIGS. 5A-5B, the outersurfaces of the third jig 324 is slid within the inner open portion ofthe second jig 322 and in the depressions 340, 342 formed on the innersurface therein. The outer surfaces of the second jig 322 are slidwithin the inner open portion of the first jig 320 and into thedepressions 330, 332 formed therein. As noted above, the jigs 320-324may be held together with selected fixation mechanisms, includingadhesives, fasteners, interference or snap fits, etc.

It is understood, however, as noted above, that a robotic mechanism mayknow the precise position of both the first jig member 320 and thesecond jig member 322 such that the stops 348 and 350 are not required.Nevertheless, the stops 348 and 350 are disclosed herein for the currentdiscussion. The stops 348 and 350 may provide an indication that thesecond jig member 322 is positioned in an appropriate location relativeto the first jig member 320 and that the assembly is complete such thatthe common center 310 has been achieved.

With reference to FIGS. 3A-5B, the coil group 266 may be assembled forinclusion in the coil array 264. It is understood that at least three ofthe coil groups can be assembled as illustrated in FIGS. 3A-5B andincluded in the coil array 264, as illustrated in FIG. 2. It is furtherunderstood, however, that any appropriate number of coil groups need beincluded in the selected coil array, which may include more than threecoil groups 266A-266C or less than three coil groups.

Further, it is understood that the jigs 320-324 allow for a modularcreation of each of the three coil portions 300-304 that form the coilgroup 266. Thus, each of the jigs 320-324 may be wound with conductivematerial, such as copper wire having a gauge of about 22 AWG to about 32AWG (including an outer diameter of about 0.65 mm to about 0.2 mm). Itis understood, however, that wire of any appropriate gauge may beselected depending up selected field configurations, power, etc. Thejigs 320-324 may be individually wound separately and then assembledtogether to form the final coil group 266, as illustrated in FIGS.3A-5B. Thus, the formation of the individual coil portions on therespective jigs 320-324 can occur in an appropriate manufacturingtechnique and step without requiring the formation of all three coils,for forming the coil group 266, substantially simultaneous or a fixedsequential manner.

The various coil portions 300-304, as discussed above, can include thecoil portion 300 as illustrated in FIGS. 6, 7A, and 7B. As discussedabove, the first coil portion 300 can include the jig 320. The jig 320and the coil of wire placed thereon is discussed here, but it isunderstood that a similar process and details may be included on anyappropriate jig.

The jig 320 can include a first external wall 380 that can form the topsurface 354 and a second external wall 382. Between the first externalwall 380 and the second external wall 382 can be a main coil orconductive material groove or channel 390. The main groove 390 may alsoinclude an external wall 391. As discussed herein, a wire may be woundaround the jig 320 and on the external wall 391 to form the coil portion300. A current driven through the wire will generate the EM field, asdiscussed above.

According to various embodiments, as illustrated in FIGS. 6, 7A, and 7B,the main groove or channel 390 can include one or more sub-walls orinternal walls 392 formed therein. Positioned between the exterior walls380, 382 and the internal walls 390 can be a coil, including a pluralityof windings, of conductive material, such as winds of a wire 393discussed above. The wire may be wound in sub-grooves 394 formed betweeneach of the sub-walls 392 and the respective sub-walls 392 and externalwalls 380, 382. The small or sub-grooves 394 can be further at leastpartially formed or defined by a surface 396 of the jig 320 including asurface grooves 398. The grooves, including the surface grooves 398 andthe sub-grooves 394, may allow the windings to be manually wound aroundthe jig 320 in a substantially repeatable manner. Generally, about 5-10,including about 8-10 windings can be formed in each of the sub-grooves394 and surface grooves 398 around the jig 320. It is understood thatmore or less windings can be provided within the respective groovesdepending upon the field strength selected to be formed by the coilportion 300. Each winding group, such as between the walls 392 may beconnected to the other winding groups so that the coil portion 300 formsa single coil. Further, the jig 320 can include an exit spot or portion400 to allow the leads 402, 404 of the wire formed on the jig 320 forconnection to control portions, such as the CAC controller 260. Thesub-grooves 394, and surface grooves 398 can allow for ease ofrepeatability of forming coils on the jig 320.

As illustrated in FIG. 7B, the wire 393 may be wound in a plurality ofwindings 393 a-393 e, any appropriate number of windings may beincluded. Further, a first row of windings 395 a (i.e. winding group)may be separated and spaced apart from a second row of windings 395 b(i.e. winding group) by one of the walls 392. The two winding groups 395a, 395 b may be connected, as noted above. Any appropriate number of thewindings groups may be provided on the jig 320 and all may be connected.It is understood, however, as discussed herein, that the severalwindings need not be so separated from one another. Further, theexternal walls 380, 382 may be co-extensive or extend beyond thewindings, as illustrated in FIG. 7B.

Further, the jig 320, or other jig portions, may include one or more ofthe surface grooves 398. The surface grooves allow the first winding ofeach winding portion to be at least partially, and even completely,recessed into the surface of the main groove 390. Thus, as the wirewinding moves from one of the sub-grooves 392 to another sub-groove 394the wire may be first recessed. Successive windings, therefore, may beflatter and smoother through the transition. This surface groove 398,therefore, allows the coil to be smoother, more even, and not include abump in the transition area. Thus, field created by the coil portion 300may be more uniform and more repeatable between coil forms.

It is further understood that the jig 320 may be wound in a plurality ofmanners. As described above, the surface groove 398 may assist inassuring a flat transition area if each successive winding moves to anadjacent sub-groove. It is understood, however, that the coil portion300 may be formed by completely winding each sub-groove before windingin another adjacent sub-groove. Or each sub-groove may have a selectednumber of windings, such as two or three, then the next sub-groove, andthen the jig may be wound back again.

In providing a substantially repeatable and/or uniform configuration ofthe coil wire from one manufactured coil portion to another manufacturedcoil portion, calibration may be performed more efficiently and/orsubstantially minimized or reduced in time for calibrating the TCA 264.The jigs 320-324, therefore, allow the coil portions 300-304 to bemanufactured with tight or small tolerances. As discussed above, thewinding of the coil portion 300 with a conductive material can beperformed for each of the coil portions including each coil portion fora plurality of the coil groups that may be included in the TCA 264.Accordingly, the illustration of the coil portion 300 in FIGS. 6 and 7is merely exemplary.

With additional reference to FIG. 8, an alternative configuration of thecoil portion 300 as illustrated as coil portion 300′. The coil portion300′ may include portions that are substantially similar to the coilportion 300, including the jig 320 as discussed above. A jig 320′,however, of the coil portion 300′, may include only the external wall380′ and the external wall 382′ while not having any internal walls 392.A plurality of windings of the wire 393 may be sequentially formed onthe jig 320′, however, using various winding techniques and/ormechanisms. Winding machines such as the Star Winder, sold by GormanMachine having a place of business in MA, can be programmed tomanipulate the jig 320′ to neatly and uniformly form windings and layersof coils of the connective material within the main groove 390′ withoutincluding the internal walls 392.

The main groove 390′ can maintain the multiple coils within or on thejig 320′ while the winding machine can be programmed to move theconductive material or the jig 320′, or both, to form the stacked coilson the jig 320′. The coils may be wrapped on each other or stacked onone another, as illustrated in FIG. 7B without the wall 392. The wire393 may further include an adhesive coating to assist in maintaining thewound configuration. The windings of the conductive material on the jig320′, however, may be substantially similar as the windings formed onthe jig 320 that includes the internal walls 392, but not separated bythe walls 392.

The substantially precise and neat winding, e.g. with tight tolerances,of the conductive material on the jig 320′ can allow for repeatabilitybetween the coil portions manufactured at different times, as discussedabove. The repeatability can assist in reducing calibration time and/oreliminating calibration time. As discussed above, the calibration can becalibration after manufacturing to identify the shape of the field anddetermine variability of the field strength therein for navigation.

According to the various embodiments, including those discussed above,the transmitter coil array 264 of the navigation system 202 may beformed to generate or emit an electromagnetic field to define anavigation space relative to a subject, such as the human subject 152.In providing the plurality of modular jig members 320-324, coil portions300-304 that form the coil groups 266 can be formed separately andseparately assembled according to a selected manufacturing technique andprocess, including that discussed above. Therefore, forming two or morecoils of wire for the TCA 264 substantially simultaneously or during asingle processing step need not occur. The various coil portions can beformed separately and then efficiently, as illustrated in FIGS. 5A and5B, assembled together. The assembly can then be provided in forming theTCA 264 for emitting a field for navigation. This can allow forminimizing manufacturing steps and simply efficiently forming jigs toform single coils.

Moreover, the coils may be manually wound or rewound for variouspurposes with small tolerances. Although, according to variousembodiments, the jigs 320-324 may be formed to allow for substantiallyautomatic or machine winding of the single coil portions, withoutrequiring intricate manipulation of a jig to form the coil group 266, asdiscussed above. The separate coil portions can be assembled, asdiscussed above, for forming the coil group 266 and subsequently formingthe TCA 264. This can allow a method of forming the first coil portion300, forming the second coil portion 302, and forming the third coilportion 304, and then assembling the first coil portion 304 into thesecond coil portion 302 and then assembling the assembly of the firstand second coil portions into the third coil portion 300. Such a methodallows for a modular construction of the coil group 266 for variouspurposes.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A system for navigating an instrument,comprising: a first coil jig having at least a single first coil ofconductive material positioned thereon; a second coil jig having atleast a single second coil of conductive material positioned thereon;and a third coil jig having at least a single third coil of conductivematerial positioned thereon; wherein the first coil jig is configured tobe assembled with the second coil jig and the second coil jig isconfigured to be assembled with the third coil jig to form together acoil group having connected together the first coil jig, the second coiljig, and the third coil jig, wherein the first coil jig includes (i) afirst external wall spaced apart from (ii) a second external wall and amain coil channel defined between the first and second external walls,and wherein the main coil channel (i) includes a depth between the firstexternal wall and the second external wall that is configured to havewrapped at least the single first coil of conductive material and (ii)having at least eight surfaces formed between the first and secondexternal walls to create faceted corners to allow at least the singlefirst coil to be wrapped according to selected tolerances about the atleast eight surfaces to at least assist in modeling the field formed byat least the single first coil of conductive material formed on thefirst coil jig.
 2. The system of claim 1, wherein the coil groupincludes a common center for each of the first coil jig, the second coiljig, and the third coil jig.
 3. The system of claim 1, wherein the firstcoil jig, the second coil jig, and the third coil jig are all separatefrom one another.
 4. The system of claim 1, wherein the main coilchannel includes at least one internal wall that forms at least onesub-groove formed within the at least one of the eight surfaces of themain coil channel, and wherein the sub-groove is configured to receive afirst conductive material to form at least the single first coil ofconductive material.
 5. The system of claim 4, wherein the sub-grooveincludes a plurality of sub-grooves formed parallel to each otherbetween the first and second external walls.
 6. The system of claim 5,wherein the second jig includes (i) a third external wall spaced apartfrom (ii) a fourth external wall and a second main coil channel definedbetween the third and fourth external walls, wherein the second maincoil channel (i) is configured to receive at least the single secondcoil of conductive material and (ii) having at least eight surfacesformed between the third and fourth external walls to create facetedcorners to allow at least the single second coil to be wrapped accordingto selected tolerances about the at least eight surfaces to at leastassist in modeling the field formed by at least the single second coilof conductive material formed on the second jig; and wherein the thirdjig includes (i) a fifth external wall spaced apart from (ii) a sixthexternal wall and a third main coil channel defined between the fifthand sixth external walls, wherein the third main coil channel (i) isconfigured to receive at least the single third coil of conductivematerial and (ii) having at least eight surfaces formed between thefifth and sixth external walls to create faceted corners to allow atleast the single third coil to be wrapped according to selectedtolerances about the at least eight surfaces to at least assist inmodeling the field formed by at least the single third coil ofconductive material formed on the third jig.
 7. The system of claim 1,wherein each of the first coil jig, the second coil jig, and the thirdcoil jig include an open center; wherein the first coil jig is receivedwithin a first open center of the second coil jig, wherein the secondcoil jig is received within a second open center of the third coil jig,and wherein the second coil jig is received within the second opencenter of the third coil jig with the first coil jig received within thefirst hollow center.
 8. The system of claim 1, further comprising: anavigation system including a tracking system having the transmittercoil array; and a tracking device configured to be tracked with a fieldgenerated by the transmitter coil array.
 9. The system of claim 8,wherein the coil group includes a plurality of coil groups.
 10. Thesystem of claim 1, wherein the first coil jig includes a first stopmember extending from an exterior surface of the first coil jig, whereinthe first stop member is configured to engage a second exterior surfaceof the second coil jig in the coil group.
 11. The system of claim 1,wherein the first coil jig having at least the single first coil ofconductive material positioned thereon includes at least the singlefirst coil of conductive material being wound on the first coil jig,wherein the second coil jig having at least the single second coil ofconductive material positioned thereon includes at least the secondfirst coil of conductive material being wound on the second coil jig,and wherein the third coil jig having at least the single third coil ofconductive material positioned thereon includes at least the singlethird coil of conductive being is wound on the third coil jig.
 12. Asystem for navigating an instrument, comprising: a transmitter coilarray having a coil group, including wherein the coil group includes: afirst coil portion having a first jig with at least a single first coilof conductive material positioned thereon, a second coil portion havinga second jig having at least a single second coil of conductive materialpositioned thereon, and a third coil portion having a third jig havingat least a single third coil of conductive material positioned thereon,wherein the coil group is formed by the first coil jig assembled withinthe second coil jig, and the second coil jig having the first coil jigassembled therein is assembled with the third coil jig; a trackingdevice configured to sense a field generated by the transmitter coilarray; a navigation processor configured to execute instructions todetermine a position of the tracking device; and a display deviceconfigured to display a representation at the determined position of thetracking device, wherein the first coil jig includes (i) a firstexternal wall spaced apart from (ii) a second external wall and a maincoil channel defined between the first and second external walls,wherein the main coil channel (i) includes a depth that is configured tohave wrapped at least the single first coil of conductive material and(ii) having at least eight surfaces formed between the first and secondexternal walls to create faceted corners to allow at least the singlefirst coil to be wrapped according to selected tolerances about the atleast eight surfaces to at least assist in modeling the field formed byat least the single first coil of conductive material formed on thefirst coil jig.
 13. The system of claim 12, further comprising: aninstrument associated with the tracking device, wherein therepresentation includes an icon displayed with the display device. 14.The system of claim 12, wherein the second jig includes (i) a thirdexternal wall spaced apart from (ii) a fourth external wall and a secondmain coil channel defined between the third and fourth external walls,wherein the second main coil channel (i) is configured to receive atleast the single second coil of conductive material and (ii) having atleast eight surfaces formed between the third and fourth external wallsto create faceted corners to allow at least the single second coil to bewrapped according to selected tolerances about the at least eightsurfaces to at least assist in modeling the field formed by at least thesingle second coil of conductive material formed on the second jig, andwherein the third jig includes (i) a fifth external wall spaced apartfrom (ii) a sixth external wall and a third main coil channel definedbetween the fifth and sixth external walls, wherein the third main coilchannel (i) is configured to receive at least the single third coil ofconductive material and (ii) having at least eight surfaces formedbetween the fifth and sixth external walls to create faceted corners toallow at least the single third coil to be wrapped according to selectedtolerances about the at least eight surfaces to at least assist inmodeling the field formed by at least the single third coil ofconductive material formed on the third jig.
 15. The system of claim 14,wherein the third jig includes an open center formed by an internalsurface, and wherein the third jig further includes at least onedepression formed within the internal surface to operably engage thesecond jig in the coil group.
 16. The system of claim 15, wherein thesecond jig includes a stop portion to limit movement of the second jigrelative to the third jig.
 17. A method of forming a localizer fornavigating an instrument with a system, comprising: forming a coil groupby: positioning at least a single first coil of conductive material on afirst coil jig, wherein the first coil jig includes (i) a first externalwall spaced apart from (ii) a second external wall and a first main coilchannel defined between the first external wall and the second externalwall, and wherein the first main coil channel (i) includes a depthbetween the first external wall and the second external wall that isconfigured to have wrapped therein at least the single first coil ofconductive material and (ii) having at least eight surfaces formedbetween the first and second external walls to create faceted corners toallow at least the single first coil to be wrapped according to selectedtolerances about the at least eight surfaces to at least assist inmodeling the field formed by at least the single first coil ofconductive material formed on the first coil jig; positioning at least asingle second coil of conductive material on a second coil jig;positioning at least a single third coil of conductive material on athird coil jig; assembling together the first coil jig, the second coiljig, and the third coil jig.
 18. The method of claim 17, furthercomprising: generating a field with the coil group.
 19. The method ofclaim 18, further comprising: sensing the generated field with atracking device.
 20. The method of claim 17, further comprising: sensinga field with the coil group generated with a tracking device.
 21. Themethod of claim 17, wherein assembling together the first coil jig, thesecond coil jig, and the third coil jig includes placing the first coiljig and the second coil jig within the third coil jig.
 22. The method ofclaim 21, wherein assembling together the first coil jig, the secondcoil jig, and the third coil jig includes: forming a sub-assembly byassembling the first coil jig within an opening formed by the secondcoil jig, and assembling the sub-assembly of the first coil jig and thesecond coil jig within an opening formed by the third coil jig; whereinthe second coil jig includes (i) a third external wall spaced apart from(ii) a fourth external wall and a second main coil channel definedbetween the third and fourth external walls, wherein the second maincoil channel (i) is configured to receive at least the single secondcoil of conductive material and (ii) having at least eight surfacesformed between the third and fourth external walls to create facetedcorners to allow at least the single second coil to be wrapped accordingto selected tolerances about at least the eight surfaces to at leastassist in modeling the field formed by at least the single second coilof conductive material formed on the second coil jig; and wherein thethird coil jig includes (i) a fifth external wall spaced apart from (ii)a sixth external wall and a third main coil channel defined between thefifth and sixth external walls, wherein the third main coil channel (i)is configured to receive at least the single third coil of conductivematerial and (ii) having at least eight surfaces formed between thefifth and sixth external walls to create faceted corners to allow atleast the single third coil to be wrapped according to selectedtolerances about the at least eight surfaces to at least assist inmodeling the field formed by at least the third single coil ofconductive material formed on the third coil jig.